The spleen is found on the left side of your body, behind the stomach on a level with the 9th to 11th ribs. It is similar in structure to a lymph node and is the largest lymphatic organ in the body. The spleen contains two main types of tissue - white pulp and red pulp. White pulp is lymphatic tissue (material which is part of the immune system) mainly made up of white blood cells. Red pulp is made up of blood-filled cavities (venous sinuses) and splenic cords. Splenic cords are special tissues which contain different types of red and white blood cells.